Previous studies have shown that the endothelium of cat, dog and primate cornea has a lesser regenerative capacity than that of rabbit and is probably more similar to that of man. The proposed studies will compare regenerative capacity in young and aged rats, puppies and dogs and normal and buphthalmic rabbits in order to determine if differences occur due to age or degeneration. Transcorneal freezing with brass probes cooled in liquid nitrogen will be used to destroy the central 50 per cent of endothelial cells in each animal. The regeneration of the endothelium will be studied by biomicroscopy, scanning and transmission electron microscopy, autoradiography of the incorporation of tritiated thymidine into aqueous humor factors on endothelial regeneration will also be studied. The barrier function of the endothelium will be evaluated in corneas in which the endothelium has regenerated following freezing injury. BIBLIOGRAPHIC REFERENCES: Van Horn, D.L. and Hyndiuk, R.A.: Endothelial wound repair in primate cornea, Exp. Eye Res. 21:113-124, 1975. Van Horn, D.L., Hyndiuk, R.A., Seideman, S., Buco, P.J., and DeBruin, J: Endothelial regeneration in cornea: Comparative study in rabbit and cat, Scanning Electron Microscopy, 1976 (O. Johari and I. Corvin, eds.).